Re: vc-modify-change-comment for "modern" backend fix

[Alfred M. Szmidt]

On a similar thread, log-view-extract-comment is not really extensible
for other VCS's.

Ideally, this should get the actual commit message directly from the
backend for a file / revision; but there is no good function for doing
that -- vc-print-log is the closest, but the output of that depends on
the backend.

What would be the best way to go about getting just the commit message
in a semi-backend-agnostic manner?